Please help me with this partial derivative, Im stuck in Cal III

At an Oregon fiber-manufacturing facility, an analyst estimates that the weekly number of pounds of acetate fibers that can be produced is given by the function: z = f(x, y) = 14500x + 4000y + 15x2y - 13x3 Where: z = the weekly # of pounds of acetate fiber x = the # of skilled workers at the plant y = the # of unskilled workers at the plant Determine the following: A) The weekly number of pounds of fiber that can be produced with 16 skilled workers and 32 unskilled workers. Answer = pounds B) Find an expression (fx) for the rate of change of output with respect to the number of skilled workers. Answer = fx = C) Find an expression (fy) for the rate of change of output with respect to the number of unskilled workers. Answer = fy = D) Find the rate of change of output with respect to skilled workers when 16 skilled workers and 32 unskilled workers are employed. (Your answer will be a number.) Answer = weekly pounds per skilled worker E) Find the rate of change of output with respect to unskilled workers when 16 skilled workers and 32 unskilled workers are employed. (Your answer will be a number.) Answer = weekly pounds per unskilled worker